Rick's Free Auto Repair Advice

Synthetic Oil Facts and Myths

Should you switch to synthetic oil

synthetic oil, valvoline, mobil 1, royal purple, amzoil, penzoil, castrol, quaker state

This article is about synthetic oil and the myths surrounding its use. It’s just one in a series. If you’d like to know more about synthetic oil click on the links below.

Choosing the right motor oil

Chrysler’s 3.5-liter engine has oil sludge issues

High mileage oil and oil filters

Oil Viscosity Warning

Synthetic Oil Facts and Myths

Synthetic oil versus conventional oil

What motor oil to use

What oil brand is best

What oil should you use

When to change oil

Best Oil filter

I’m asked these questions about synthetic oils on a regular basis, so I thought I’d take the time to separate fact from fiction.

Myth #1 You should flush the engine before you switch to synthetic

NO! The rationale for this myth is that synthetic oil contains more detergents than conventional oil. That particular fact is true—they do contain more detergent. However, synthetic oils also contain higher levels of dispersant additive. The dispersant is what keeps the dirt in suspension and carries it off to the filter. In other words, synthetic oil doesn’t dissolve buildup and then just drop it at the bottom of the engine.

Now, let’s address the flushing issue. If you’ve been maintaining your vehicle according to the manufacturer’s recommendations, you won’t have sludge buildup. In that case, flushing your engine is a complete waste of time and money. If you’ve neglected your engine, flushing it is the WORST thing you could do. See my article “Engine Flush=Wallet Flush” to see what kind of catastrophic damage you can do to a sludged-up engine by flushing it.

The bottom line is this: DON’T flush a well-maintained engine before switching to synthetic, and DON’T flush a poorly maintained engine in the hope that you can bring it back from hell.

Myth #2 Switching to synthetic will cause my engine to leak

This was true when synthetic motor oils first came out. Those oils were designed for racing. Racing oils don’t need seal conditioners, dispersants, or detergent additives because they’re changed after every race. But when people used those racing oils in their daily drivers, the lack of seal conditioners caused gaskets and seals to leak.

Seal conditioners soften the seals and actually make them swell. If an aged engine seal returned to its hardened state, it can leak. But since synthetic oils flow easier when cold, that only compounded the problem. The engine parts on a cold engine contract. Add in hardened seals and a thinner oil and guess what—you get leaks.
But today’s synthetic oils have the same seal conditioners as conventional oil. So if someone tells you that switching to synthetic will cause your engine to leak, tell them their information is outdated by about 25 years.

Myth #3 You can go longer between oil changes if you switch to synthetic

What this myth based on? I mean, really, what is it about synthetic oil that makes people think it can last 25,000 miles? Synthetic oil in an engine designed for synthetic can go longer between oil changes. But the oil experts I’ve interviewed (and I’ve interviewed quite a few) tell me that no synthetic oil will show serviceable levels of ALL the necessary additives once you go beyond the manufacturer’s recommended oil drain intervals.

Let’s say you send your oil in for an analysis (cost is around $25 which defeats the purpose of the test in the first place). The analysis comes back and shows low “wear metals,” so you automatically make the assumption that the friction modifiers are still working. You may be right. But when you read the report and move over to the additives portion of the report, you run into a brick wall. Why? Because you don’t know what the base level is for those additives. Unless you have insider information, the numbers mean nothing if you view them as a snapshot. They only mean something over time. So you can test the oil every 5,000 miles and see how the additives are holding up over time. But you’ll spend $25 on each test. In the meantime, the viscosity improvers, anti-oxidant, anti-foaming, friction modifiers, and dispersants are constantly wearing out. Even if the lab results show little metal wear, worn oil reduces gas mileage and increases engine emissions. Oil experts tell me that they’ve seen people run extended drain intervals up to 25,000 miles and then fail a state emissions test. Where’s the economy in that?
Bottom line. The only way to reliably run extended drain intervals is to test your oil on a regular basis. That will cost you far more than just changing it according to the manufacturer’s recommendations.

Myth #4 Once you switch to synthetic, you can’t go back to traditional oil

Really? You mean the engine gets used to the diet of synthetic and will throw a temper tantrum if you feed it conventional oil? There is NO truth to this rumor. None. Nadda. Zip. It’s a myth—plain and simple. Go ahead and switch back and forth as much as you want.

Myth #5 Since synthetic oils flow better at cold temps, you can bump up to the next higher viscosity.

We all know that you want a thicker oil to protect your engine at higher temps. So, if the manufacturer recommends 5W-30, should you move up to 10W-30 if you’re running synthetic? NOPE. It’s true that synthetic 5W oil flows better than conventional 5W oil. But it’s not true that a 10W synthetic flows as well as a 5W conventional. And that thicker oil can really screw up variable valve timing mechanisms—even resulting in a Check Engine light. Trust me, the manufacturers have done a lot of research on this. If they want you to use 5W-30, don’t think you can outsmart them.


© 2012 Rick Muscoplat


Posted on by Rick Muscoplat

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